Zirconia particles can be added to an organic matrix such as a polymeric material to increase the index of refraction or x-ray opacity of the organic matrix while retaining the optical transmission of the organic matrix. The extent to which the x-ray opacity and/or refractive index of the organic matrix can be increased is dependent on the percent loading of zirconia in the organic matrix and on characteristics of the zirconia particles such as the percent crystallinity, the crystalline structure, the primary particle size, and the degree of association between primary particles.
Crystalline zirconia usually has a higher refractive index and a greater x-ray scattering capability than amorphous zirconium-containing materials. The optical transmission is often a function of the size of the zirconia particles. As the primary particle size increases and/or the degree of association between primary particles increases, the optical transmission can be reduced. The percent loading limit of zirconia particles in an organic matrix material is usually a function of both the extent of particle association and the particle aspect ratio. As the extent of particle association increases, the percent loading limit of the zirconia particles in an organic matrix tends to decrease. Similarly, as the aspect ratio of the zirconia particles increases, the percent loading limit of the zirconia particles in an organic matrix tends to decrease.